U.S. Pat. No. 6,941,910 shows how a summation lever can be used to combine the motion of two cam profiles in order to produce valve lift, and how the valve lift may be controlled by changing the relative phasing of the two cam profiles. The latter patent also teaches how phasing of the cam lobes relative to each other may be achieved by mounting them on the inner shaft and an outer tube of an assembled camshaft, termed an SCP (single cam phaser) camshaft, which has one set of lobes fixed for rotation with the outer tube and a second set fast in rotation with the inner shaft.